Hundreds of activists took the streets of cities on the northern Japanese island of Hokkaido on Sunday under more than 20,000 police security as leaders from the top industrialized nations arrived for their annual summit.

The discussions of this year’s three day gathering open at the Windsor Hotel, close to Lake Toyako, on Monday morning, with the leaders of the United States, Japan, Germany, France Britain, Italy, Canada and Russia joined by 14 other heads of state in what is the biggest ever G8 meeting. Beside the impressive number of police officers called out, Japan mobilized the coast guard and reportedly even conducted flights over the designated area with fighter jets.

The Japanese government is so afraid of incident or attack that cities as far away as Tokyo have also been under close security for over a week with more than 40,000 police officers spread all over the region. This summit will be U.S. President George W Bush's final G8 meeting, thus being considered a primary target for a possible terrorist attack.

"We have three policies: Be visible, be ready and keep the pressure on," a senior police official in charge of security, speaking on condition his name not be disclosed, said on the public broadcaster NHK.

Practically no one except the G8 leaders and their operators are being permitted anywhere near the actual summit site, which is at an isolated lakeside hot springs resort deep in the forests of Japan's northern island of Hokkaido.

Media makes no exception, being an hour's drive away and having to rely on closed-circuit TV to spot the event.

In spite of the local police and immigration authorities efforts, several thousand overseas demonstrators have teamed up with home-grown protesters to rail against everything from global warming to stopping use of cluster bombs, poverty and even the G8 itself.

On a banner put up at a demonstration event in the vicinity Sapporo, the island’s most important city, was written: "No to the hypocritical G8 Summit promoting the destruction of the global environment." Another banner said: "Down with imperialism."

Compared to the protests on Saturday, when around 5,000 demonstrators were escorted through Sapporo by hundreds of police in full riot gear, this one has been more relaxed.

Four people, including a media photographer, were arrested and anti-globalisation activists accused the police of being "heavy-handed."